Wearable blood pressure monitoring system

ABSTRACT

An apparatus includes one or more memories storing computer readable code and processor(s). The processor(s), in response to loading and executing the computer readable code, cause the apparatus to perform operations including receiving electrocardiogram data from an electrocardiogram sensor. The electrocardiogram data includes data from an electrocardiogram from a person. The operations also include receiving pulse wave data from one or more pulse wave pressure sensors. The pulse wave data includes data from one or more pulse waves from the person. The operations further include determining blood pressure using the electrocardiogram data or the pulse wave data from the chest and the pulse wave data from the wrist or finger, and outputting an indication of the blood pressure. Another apparatus uses pulse wave data from two pulse wave sensors (e.g., pulse wave pressure sensor(s) and/or PPG sensor(s)) and blood pressure determinations are made using these pulse wave data.

BACKGROUND

This invention relates generally to sensors and, more specifically,relates to wearable sensors.

Abbreviations used in the specification and/or drawings are definedbelow, prior to the claims.

Today, monitoring of personal health and wellness from detecting anearly onset of a disease to monitoring recovery from medicalintervention can be infrequent and/or costly. For instance, one riskfactor for cardiovascular disease (CVD) is high blood pressure.Typically, high blood pressure develops over a long time period and maynot be found until substantial damage has been done. Monitoring bloodpressure in real time and in a remote mode could help reduce, prevent,or cure certain cardiovascular diseases.

SUMMARY

The following summary is merely intended to be exemplary. The summary isnot intended to limit the scope of the claims.

In one example, an apparatus includes one or more memories storingcomputer readable code and one or more processors. The one or moreprocessors, in response to loading and executing the computer readablecode, causing the apparatus to perform operations comprising: receivingelectrocardiogram data from an electrocardiogram sensor, theelectrocardiogram data comprising data from an electrocardiogram from aperson; receiving pulse wave data from at least one pulse wave pressuresensor, the pulse wave data comprising data from one or more pulse wavesfrom the person; determining blood pressure using at least theelectrocardiogram data and the pulse wave data; outputting an indicationof the blood pressure.

In another example, an apparatus comprises one or more memories storingcomputer readable code and one or more processors. The one or moreprocessors, in response to loading and executing the computer readablecode, causing the apparatus to perform operations comprising: receivingfirst pulse wave data from a first pulse wave sensor placed at a firstlocation on a person, the first pulse wave data comprising data from oneor more pulse waves from the first location of the person; receivingsecond pulse wave data from a second pulse wave sensor placed at asecond location on the person, the first and second locations beingdifferent locations on the person, the second pulse wave data comprisingdata from one or more pulse waves from the second location of theperson; determining blood pressure using at least the first and secondpulse wave data; and outputting an indication of the blood pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system used on a human being (i.e., a person) todetermine information used for an estimate of blood pressure;

FIG. 2 is a graph on the same time scale of an ECG wave and a radialartery pulse wave, and illustrates determination of pulse transit time(PTT) between heart and wrist and time difference between a forward wavepoint and the ending point of the wave (T₂);

FIG. 3 is an example of a possible wearable blood pressure monitoringsystem interfacing with a network and server;

FIG. 4 illustrates a technique for determining a time difference betweena forward wave point and a reflective wave point, ΔT_(DVP);

FIG. 5, which includes both FIGS. 5A and 5B, illustrates the peripheral(radial) pressure in mmHg over time in seconds (s) for a young person(FIG. 5A) and an old person (FIG. 5B);

FIG. 6 illustrates a cross-section of an individual pulse wave pressuresensor of a double-layered sensor;

FIG. 7 is a cross section of a possible example of a layered andmulti-sectional pulse wave pressure sensor structure; and

FIG. 8. is a graph on the same time scale of two different pulse waves,and illustrates determination of pulse transit time (PTT) between heartand wrist and time difference between a forward wave point and theending point of the wave (T₂).

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. All of the embodiments described inthis Detailed Description are exemplary embodiments provided to enablepersons skilled in the art to make or use the invention and not to limitthe scope of the invention which is defined by the claims.

It is possible to provide an estimate of blood pressure for a humanbeing (i.e., a person) by using data from an electrocardiogram (ECG) andat least one photoplethysmography (PPG) (also called photoplethysmogram)sensor, which is usually implemented as an oximeter. Referring to FIG.1, this figure illustrates a system used on a human being 160 todetermine information used for an estimate of blood pressure. Humanbeing 160 is also referred to as a person herein. An ECG sensor 105comprises ECG circuitry 130, wiring 120, and three electrodes RA 110-1,LL 110-2, and LA 110-3. The electrodes 110 are formed in a triangle 180in this example. The ECG circuitry 130 forms ECG wave data 135 (which isdata describing electrical signals from the heart 168 and is in mV,millivolts) using information from the electrodes 110. Also shown is apulse wave sensor 155, which includes a PPG or oximeter sensor 175 andPPG or oximeter circuitry 160. The PPG or oximeter circuitry 160 createsradial artery pulse wave data 165 (based on blood flow in the artery190) from the PPG or oximeter sensor 175. A PPG unit will determinerelative blood absorbance versus time (which also indicates relativeblood volume versus time). The oximeter unit determines a percentage ofoxygen saturation in the artery. Here, R_(P), R_(D), H_(P), and H_(D)are the maximum R peak of ECG pulse wave, the distance of aortic valveposition, the starting point of radial artery pulse wave, and thedistance of radial wrist position, respectively. Also, the circle 166and the solid line 190 are the exact position of aortic valve and therough distance from aortic valve to wrist, respectively. This figure isfrom D-H Nam, et al., “Measurement of Spatial Pulse Wave Velocity byUsing a Clip-Type Pulsimeter Equipped with a Hall Sensor andPhotoplethysmography”, Sensors 2013, 13, 4714-4723.

Turning to FIG. 2, this figure is a graph on the same time scale of anECG wave data 135 and a radial artery pulse wave data 165. Thisparticular exemplary radial artery pulse wave data 165 was determinedusing photoplethysmography (PPG) (e.g., a photoplethysmogram), however,this data may also be determined using the pressure sensors describedherein. The pulse transit time (PTT) 195 may be determined by comparingthe R peak 203 of the ECG wave data 135 and the corresponding maximuminclination 204 of the radial artery pulse wave data 165. See, forinstance, P. Fung et al., “Continuous Noninvasive Blood PressureMeasurement by Pulse Transit Time”, Proceedings of the 26th AnnualInternational Conference of the IEEE EMBS San Francisco, Calif., USA(Sep. 1-5, 2004): “PTT in this paper is defined as the time between theECG R peak and the corresponding maximum inclination in the PPG.” The T₂197 is described below.

Using the PTT and additional information such as pulse wave velocity(PWV), height of a person, and body correlation factors, the person'sblood pressure can be determined. For instance, see the P. Fung articlecited above; H. Gesehe et al., “Continuous blood pressure measurement byusing the pulse transit time: comparison to a cuff based method”,European Journal of Applied Physiology, Volume 112, Issue 1, pp 309-315(January 2012); and S. Fuke et al., “Blood pressure estimation frompulse wave velocity measured on the chest”, 35th Annual InternationalConference of the IEEE EMBS Osaka, Japan (3-7 Jul., 2013).

While these are useful tools, they can be improved upon. For instance,exemplary embodiments here provide a wearable blood pressure monitoringsystem with a wearable ECG (electrocardiogram) on, e.g., the chest and awearable pressure sensor on, e.g., the wrist. The wearable pressuresensor on the wrist can generate more precise artery pulse waves than atypical photoplethysmography (PPG), the technique of which is oftenemployed for an oximeter. One of the highly sensitive pressure sensorsis made of elastomeric pyramids which, upon pressing and releasing,generate pulse waves in the form of a capacitance (across the pressuresensor) versus time graph. In an exemplary embodiment, an electronic hubreceives (e.g., wirelessly) ECG and pulse wave signals. Certainexemplary embodiments also include an upgraded algorithm that canprovide an output of more precise blood pressures which can betransferred (e.g., wirelessly) to, for instance, a cognitive/cloudsystem that in turn may communicate with hospitals, doctors, and/orusers.

Another possible aspect of the exemplary embodiments is to measure andstore a person's artery stiffness index which is indicative ofhypertension or vascular diseases. The cumulated records of bloodpressures and artery stiffness indices can be used for an earlydiagnosis and/or cure of certain cardiovascular disease(s).

One possible aspect of the exemplary embodiment includes the use of amore wearable and sensitive pressure sensor on, e.g., the wrist. Thereare at least two distinct advantages of the types of pressure sensorsused herein over the PPG or oximeter:

(1) A first advantage is better sensitivity to provide more precisepulse wave signals.

(2) A second advantage is much less power consumption since the pressuresensors used herein generate their capacitance variation by pulseswithout requiring much electrical power, while an oximeter (e.g., PPG)needs to emit light (e.g., red and infrared from LEDs) and detectreflection or transmission of the lights, which consumes a larger amountof power relative to the sensors used herein. That is, the pressuresensor still needs a little electrical power to detect capacitancevariation, but this amount of power will be much smaller than theelectrical power to emit light and detect light as in an oximeter (e.g.,PPG).

Referring to FIG. 3, this figure is an example of a possible wearableblood pressure monitoring system 300 interfacing with a network 379 andserver 395, in accordance with certain exemplary embodiments. The system300 comprises one or more wearable pulse wave pressure sensor(s) 301, awearable ECG 105, and a wearable BP hub 205. Note that some embodimentsmay also use a pulse wave sensor such as a PPG or oximeter sensor 175,and alternatively or in addition, other embodiments may use multiplewearable pulse wave pressure sensors 301. While these are consideredherein to be separate components, two or more of them may be combined.For instance, the wearable BP hub 205 and the wearable pulse wavepressure sensor 301 could be formed into a watch that is placed on thewrist. Other options are also possible, including having all threedevices in the same physical device (e.g., where the local network 279could be replaced by physical electrical connections). The components105, 205, and 301 can communicate through the local network 279, whichmay be a BLUETOOTH (a global wireless communication standard thatconnects devices together over a certain distance) or WI-FI (atechnology that allows electronic devices to connect to a wireless LAN(WLAN) network), or any other networking technology that allows devicesto communicate. Additionally, the wearable BP hub 205 is described asbeing wearable, but this may also be fixed or portable (e.g., as part ofa suite of medical instruments in a hospital). Furthermore, althougheach of the devices 105, 205, and 301 is described as being wireless andbattery-powered, one or more of them may use wirelines (e.g., vianetwork 279) to communicate, and one or more of them may also be pluggedinto another source of power (such as alternating current). The system300 in some examples interfaces with network 379 such as the Internet(or WI-FI/LAN and the Internet) and a server 395 through the wearable BPhub 205.

A wearable pulse wave pressure sensor 301 includes, in one example, oneor more processor(s) 310, a battery 305, one or more network (NW)interfaces (IIF) 330, one or more memories 315, a temperature sensor312, and a layered and multi-sectional pulse wave sensor 360-1. Eachnetwork interface 330 typically includes a transmitter (Tx) 331, areceiver (Rx) 332, and one or more antennas 333. The one or morememories include pulse wave data 165 and computer readable code 325. Inan exemplary embodiment, the one or more processors 310 execute thecomputer readable code 325 and cause the wearable pulse wave pressuresensor 301 to perform operations as described herein. In anotherexample, the operations are embedded into the one or more processors 310(or other circuitry 311), e.g., as hardware elements (such as integratedcircuits, programmable logic devices, or the like), and the one or moreprocessors 310 or the other circuitry 311 performs the operations. In afurther example, some combination of hardware or code may be used toimplement the operations described herein. A pulse wave pressure sensoris a sensor that senses blood flow via pressure of the blood (and otherparts of a person, such as skin) produced on the sensor. A pulse wavePPG sensor is a sensor that senses blood flow, typically by using green,red and/or infrared light (and other parts of a person, such as skin)produced on the sensor. A pulse wave sensor in this disclosure meanseither a pulse wave pressure sensor or a pulse wave PPG sensor.

The layered and multi-sectional pulse wave sensor 360-1 comprises amicro-controller 335, a sensor structure 355, and additional circuitry340. The micro-controller 335 comprises one or more memories 336, whichcomprise a program 337 of computer readable code and pulse wave data338. The additional circuitry 340 comprises capacitance measurementcircuitry 345 and capacitance-to-digital converter circuitry 350.Exemplary sensor structures are described below.

The sensor structure 355 may have one or multiple sections, such asthree or six sections, each section being an individual sensor unit(also called a pixel). See the examples of possible sensors in FIG. 3,6A, 6B, 8, 9, or 10 in U.S. patent application Ser. No. 14/872,209,filed on Oct. 1, 2015, by Afzali-Ardakani et al., with applicant ofInternational Business Machines Corporation.

The micro-controller 335 can execute code in the program 337 to causethe pulse wave sensor 360-1 to perform operations described herein, orthe operations can be embedded as hardware (e.g., in themicro-controller 335 or other circuitry), or some combination of thesemay be used. The micro-controller 335 can cause the capacitancemeasurement circuitry 345 to determine waveforms, for all of theindividual sensing units, capturing changes in capacitance in the sensorstructure 355 caused in response to bending of layers by a pulse waveunder the skin. The waveforms are converted to digital signals by thecapacitance-to-digital converter 350 and stored as PW data 338 in theone or more memories 336.

The one or more processors 310 can cause the pulse wave sensor 360-1 totransfer the PW data 338 to the one or more processors 310, which thenstores the data in the memory/memories 315 as pulse wave data 165. Thepulse wave data 338 and 165 may be the same or could be different,depending on implementation. For instance, the pulse wave data 338 couldbe sent in a stream or in bursts to the processor(s) 310, and theprocessors 310 would then construct the pulse wave data 165 from this,and the pulse wave data 165 could contain information from multiplepulses. The one or more processors 310 can cause the wearable pulse wavepressure sensor 301, using the one or more network interfaces 330, totransmit the pulse wave data 165 to the wearable BP hub 205 via thelocal network 279.

In another example, the wearable device 301 does not include the one ormore processors 310 or the one or more memories 315, and “only” includesthe pulse wave sensor 360-2. Pulse wave sensor 360-2 includes thebattery 305 and the network interface 330 and transmits the PW data 338to the wearable BP hub 205 via the local network 279.

The wearable ECG 105 includes one or more electrodes 110, wiring 120,ECG circuitry 130, and an ECG wave data 135 (e.g., as digital data). Thewearable ECG 105 also includes a battery 306, and one or more networkinterfaces 230, each of which typically includes a transmitter 231,receiver 232, and one or more antennas 233. The ECG circuitry 130 maycomprise one or more processors and one or more memories.

The wearable BP hub 205 includes one or more processors 210, and one ormore memories 215, a battery 307, a display 250, and one or more networkinterfaces 240, each typically comprising a transmitter 241, a receiver242, and one or more antennas 243. The one or more memories 215 includepulse wave data 165, ECG wave data 135, computer readable code 225,height data 226, BDC 227, and BP data 255. The BP data 255 is determinedusing the pulse wave data 165, the ECG wave data 135, the height data226, and the BDC data 227 as described in more detail below. In anexemplary embodiment, the one or more processors 210 execute thecomputer readable code 225 and cause the wearable pulse wave pressuresensor 301 to perform operations as described herein. In anotherexample, the operations are embedded into the one or more processors 210(or other circuitry 206), e.g., as hardware elements, and the one ormore processors 210 or other circuitry 206 performs the operations. In afurther example, some combination of hardware or code may be used toimplement the operations described herein.

The display 250 may or may not be present, but if present, may be usedto display the BP data 255, for instance. The display 250 could be LED,LCD, or any other suitable device suitable for display of information toa user. The display could also indicate that the blood pressure is toohigh (e.g., using a red color), too low (e.g., using a yellow color), oris in a normal range (e.g., using a green color). Other colors, bloodpressure, ranges, and indications may be used.

It should be noted that the data 165 and 135 are numbered the same eventhough the corresponding data exists on multiple devices. This is simplyfor ease of exposition. The data could be the same on all of the devicesor be different.

In one example, the wearable BP hub 205 determines the BP data 255(using techniques described below), and transmits the BP data 255 to aserver 395 via a wired or wireless (or both) network(s) 379 such as theInternet or the cloud. The network interface(s) 240 are typicallywireless, but could be implemented via wires. The wearable BP hub 205may also display the blood pressure and/or stiffness index (and/orpotentially other elements such as a patient's height), in addition toor in lieu of transmitting the data.

The server 395 comprises one or more processors 370 and one or morememories 380, which comprise a program 375 of computer readable code.The one or more processors 370, in response to execution of the computerreadable code in the program 375, cause the server to interact with thewearable BP hub 205 to receive the BP data 255 (and other data, such asstiffness index, indication(s) whether the BP is high, normal, low, orerror messages, and the like). The server 395 may also send out one ormore alert(s) 376, e.g., to a doctor, nurse, hospital, patient, and thelike. The doctor, nurse, hospital, and/or patient can then determine acourse of action for the patient, such as prescribing a medication, dietchange, lifestyle modification, or other action.

Although the computer system 395 is characterized as a “server”, this isonly one possibility. The computer system 395 may also be “local” to theperson using the system 300, such as being an app on the person'ssmartphone, tablet, or computer system, or on a movable cart in ahospital. In this case, the network 379 could be a local wireless (e.g.,WI-FI) or wired network. The server 395 may also be part of acognitive/cloud system that in turn may communicate with hospitals,doctors, and/or users.

The processors 210, 310, 335, and 370 and ECG circuitry 130 may be anysuitable processing device for the particular environment, such asapplication specific integrated circuits, single or multicoreprocessors, low power processors (e.g., as used in smartphones ortablets), general purpose processors, digital signal processors, and thelike. The memories 215, 315, 336, and 380 (and any memories in the ECGcircuitry 130) may be any suitable memory, such as RAM, ROM, removablememory, memories internal or external to processors, memory that retainsits values without power or only retains its values with power, and thelike.

Portions or all of a data collection and a compression algorithm may becarried out in the program 337 running on the microcontroller 335 makingthe capacitance to digital measurements. This program could be in anassembly code. This would reduce the amount of data that would need tobe transmitted (e.g., wirelessly) to the wearable BP hub 205 which wouldin turn lower the power consumption (an advantage for battery poweroperation). In the simplest example, the microcontroller 335 would knowenough not to transmit when no pulse is detected (e.g., not attached tothe patient yet), as opposed to continually transmitting capacitance todigital results. The microcontroller 335 could place the sensor 360-1into an off state (e.g., where no measurements are made and, e.g., nocurrent is passed into the capacitor(s)) in response to no pulse beingdetected. In addition, the microcontroller 335 could cause the sensor360-1 to perform measurements only periodically even if a pulse isdetected. Additionally, a temperature sensor 312 could be included andthe microcontroller could use data from the temperature sensor 312(e.g., configured to sense temperature from the skin) to determinewhether to take sensor data or not. For instance, if the temperaturereading from the temperature sensor 312 does not meet some criterion(e.g., within a few degrees of normal body temperature for a human), themicrocontroller could place the sensor 360-1 into an off state (e.g.,where no measurements are made and, e.g., no current is passed into thecapacitor(s)).

The batteries 305, 306, and 307 are used to power their respectivedevices. Each of these may be one or multiple batteries and may be anysuitable batter for this purpose. The batteries may or may not berechargeable, and it's also possible for the batteries to be replaced oraugmented with plugged-in sources of power, such as Alternating Current.

Now that an exemplary system has been described, additional detailsabout possible exemplary embodiments are described. In the exemplaryembodiments herein, the PPG can be replaced with a pressure sensor(e.g., the sensor structure 355), which has better sensitivity andenergy efficiency and is more suitable for wearable sensing devices. Inanother exemplary system, two or more pulse wave sensors can be employedwithout employing an ECG to obtain blood pressures. In this case, pulsetransit time can be obtained between two pulse wave sensors worn on twodifferent body locations (for example, one on chest and the other onwrist). Also, two new algorithms have been developed to get bothsystolic and diastolic blood pressures in a way that the diastolic bloodpressure (DBP) is dependent on the systolic blood pressure (SBP) andthat the algorithms are simplified.

An aspect of the invention includes a new algorithm for SBP, which isdifferent from that used previously (see Fuke, et al., in 35th AnnualInternational Conference of the IEEE EMBS, 2013) in which a person'sheight has not been used. The equation by Fuke, et al., isSBP=a*ln(1/PTT²)+c where a and c are constants and ln(•) means naturallogarithm. However, it is important to incorporate a subject person'sheight into the equation since the pulse transit time is related to thelength of an artery between two sensors (e.g., ECG and pulse wavesensor). The taller a person, the longer the artery from chest to wrist.The new algorithm in this invention is SBP_(PTT)=a*ln(h²/PTT²)+b where his a person's height and a and b are constants which will be empiricallyobtained and further optimized. The PTT may be determined as illustratedin reference to FIG. 2.

The new algorithm for DBP, which is another aspect of the invention, isDBP=c*SBP_(PTT)+d T₂+e where c, d and e are constants which aredetermined empirically, and T₂ is a time interval between the peak point201 of a pulse wave and the baseline point 202 where the pulse wavereaches to the baseline as shown in FIG. 2 (see T₂ 197).

In another aspect of the invention, an algorithm has been developed inorder to include a factor of an artery stiffness index so as todetermine more precise blood pressures.

One exemplary algorithm is as follows. The first equation is thefollowing:SBP=SBP_(PTT)[1+α×SI_(DVP)],

where SI_(DVP) is a stiffness index (e.g., in cm/ms), and α is definedempirically. The acronym DVP means digital volume pulse which is a wristpulse pressure.

Pulse wave velocity (PWV) is also an important factor that indicates ahealth condition. As shown in the prior art by Gesche, et al. Eur J ApplPhysiol (2011), the PWV may be calculated as follows:PWV=BDC×height/PTT,

where BDC is body correlation factor (e.g., a calibrating constantwithout units), the height (of a person) can be in cm, the PTT is pulsetransit time in ms. The height multiplied by BDC corresponds to thedistance from the sternal notch to the tip of the middle finger. The NTmay be determined as illustrated in reference to FIG. 2.

The SI_(DVP) and also a ΔT_(DVP) can be determined using the wearablepulse wave pressure sensor 301. FIG. 4 illustrates a technique fordetermining a time difference between a forward wave point and areflective wave point, ΔT_(DVP). The first curve 410 corresponds to theforwarding blood wave or the systolic blood pressure from heart to body,while the second curve 420 corresponds to the reflecting wave or thediastolic blood pressure while the arteries are contracting when theheart ventricle valve is closed. The units for FIG. 4 can be relativepressure/time if a pressure sensor is used or relative bloodabsorbance/time if a PPG is used. The third curve 430 is an envelope ofthe two curves 410+420. The SI_(DVP) may be determined as follows:

${{SI}_{DVP} = \frac{{Subject}\mspace{14mu}{height}}{\Delta\; T_{DVP}}},$

where SI_(DVP) is in cm/ms and Subject height is the height of theperson being measured, in meters. Thus, the stiffness index (SI_(DVP))is inversely proportional to the time difference between the forwardwave point and the reflective wave point (ΔT_(DVP)). It is noted thatthe stiffness index may be determined using pulse wave data from thewearable pulse wave pressure sensor 301, but may be determined usingpulse wave data from the PPG sensor 175.

It is expected that younger persons have more flexible arteries whileolder persons have stiffer arteries. This is illustrated by FIG. 5,which includes both FIGS. 5A and 5B, and which illustrates theperipheral (radial) pressure in mmHg over time in seconds (s) for ayoung person (FIG. 5A) and an old person (FIG. 5B). As can be seen theΔT_(DVP) is larger for the young person (see FIG. 5A), and is smallerfor an old person (see FIG. 5B). Thus, the stiffness index SI_(DVP) willbe smaller for the young person and larger for the old person (assumingthe same height for the person).

All the important health conditions discussed in this disclosure such assystolic/diastolic blood pressures, pulse transit times, stiffnessindices, pulse wave velocities, forward/reflective wave points can bemeasured with ECG, PPG (either transmission or reflection mode),mechanical pressure sensors and/or combinations of two or more of suchsensors. A reflection mode PPG sensor 175 likely can be more convenientin wearables, such as wrist watches and neck bands. All thedata-collection techniques including sensor handling andalgorithm-equations can also be implemented with a wide range of ECGs,PPGs, mechanical pressure sensors, and/or combinations of two or more ofsuch sensors. Furthermore, algorithms used for these health conditionscan be built into a sensor, a separate microprocessor, a smart phoneand/or a personal computer, as non-limiting examples.

Possible pulse wave sensors 360 may include the following. The design ofthe pulse wave sensor unit, in one example, includes a dielectric layerand particularly pyramid-shaped elastomeric dielectrics to maximize thechange of capacitance by the same pressure from arteries and the sensoralso involves microhairs to enhance the contact of the sensor to skin soas to enhance the detection sensitivity as shown in FIG. 6. Individualpulse wave sensor unit 360-2 includes a first layer, a skin touchingportion 910, and a second layer, sensing portion 920. Additionally,there is a third layer 971. The first, second and third layers form oneexample of a sensor structure 355. The skin touching portion 910comprises a dielectric layer 650 and dielectric microhairs 660. Thesensing portion 920 comprises conductive (e.g., metal) layers 640 and645, and dielectric pyramids 630-1. Each dielectric pyramid 630 has abase 631 and an apex 632. The conductive layers 640 and 645 anddielectric pyramids 630-1 and air in the gap form a capacitor C₂, 690-1.The third sensor layer 971 comprises conductive (e.g., metal) layers620, 625 and dielectric pyramids 630-2 and may comprise the flexiblepolymer layer 615. The conductive layers 620, 625 and dielectricpyramids 630-2 and air in the gap form a capacitor C₂, 690-2. In thisexample, the sensing portion 920 also includes a flexible polymer 635,although in other examples, the flexible polymer 635 may be assumed todivide the portions 910, 920. Combination of the flexible polymers 615,635 and 650 and the thin (30 nm-300 nm) conductive layers 620, 625, 640and 645 provides a good flexibility of the overall sensor and thus thesensor can be wearable and flexible. The individual pulse wave sensorunit 360-2 also comprises a dielectric layer 615 onto which controlcircuitry 610 is attached. The control circuitry 610 includes, in thisexample, capacitance measurement circuitry, capacitance-to-digitalconverter circuitry, a micro-controller, a memory (e.g., to store aprogram for the micro-controller and to store digitized pulse wave(s)),a battery, and a wireless communication unit. Control circuitry 610typically includes the elements 305, 330, 335, 340, and 336 from FIG. 3,and also may include the temperature sensor 312. Note that one or bothof the capacitance measurement circuitry and/or thecapacitance-to-digital converter may be implemented by themicro-controller 335. Additionally, the control circuitry 610 may use AC(alternating current) or other power source instead of or in addition toa battery. The various conductive layers 620, 625, 640, and 645 may beinterconnected via the connectors 605 and the control circuitry 610. Theconnectors 605 may be wires, metal runs on a circuit board or integratedcircuit, and the like.

In this example, the individual sensor unit 360-2 is shown contactingskin 665 of a body part 670, which contains one or more arteries 680 (ofwhich one is shown in FIG. 6). The arteries 680 generate pulse pressures675 that pass through the first and second portions 910, 920 (and thethird sensor layer 971) and cause squeezing (e.g., deformation andbending) of the elastomeric pyramids 630 of the first and secondportions 910, 920 (and the third layer 971) at least to some extent.This squeezing therefore causes a capacitance change, and the circuitry610 can determine waveforms capturing this change. Additionally, thefirst and second portions 910, 920 (and the third layer 971) areconfigured to create a capacitance change in response to a return of theportions to an original state with a release of the pulse pressure. Itis assumed that at least the elements 615 and 620 are fixed (e.g., to awatch for instance) and the squeezing occurs between the elements615/620 and the portions 910, 920, and part (e.g., elements 625, 630) of971. It is desirable that the squeezing occurs mostly with theelastomeric pyramids so that the change of the capacitance between thetwo conductive layers 645 and 640 or 625 and 620 can be maximized.

The shape of the dielectrics 630-1, 630-2 are exemplary, but use ofpyramid shapes helps to increase the pulse wave signal to noise ratio soas to improve the data quality. The dielectric pyramids 630-1, 630-2 maybe made of polymeric elastomer such as polydimethylsiloxane (PDMS). Thetwo capacitors C₁, 690-1 and C₂, 690-2 are operated in series in anembodiment.

Referring to FIG. 7, FIG. 7 is a possible example of a sensor structure355 used as a pulse wave sensor. FIG. 6 and other previous figures arealso referred to for the description of FIG. 7. In this example, thesensor structure 355 includes a polymer film 835 (e.g., a dielectric635), a Cr/Au/Cr layer 840 (e.g., conductive layer 640), an adhesivelayer 841, PDMS pyramids 890 (e.g., dielectric pyramids 630-1), a Cr/Aulayer 850 (e.g., conductive layer 645), a polymer film 855 (e.g., adielectric 650), an adhesive layer 856, and PDMS microhairs 860-1 and860-2. The sensor structure 355 has output contacts 820-1 and 821-1,which would be connected to the capacitance measurement 345. Theconductive layer 840 comprises Cr/Au/Cr. Cr promotes the adhesion to thepolymer film 835 and to the adhesive layer 841. Instead of Cr othermetals such as Ti and TiW can be used. The wiring pads 820-1 and 821-1have only Cr/Au as the surface of Au is bonded to another metal forelectrical connection. The PDMS microhairs 860-1 and 860-2 are operatedon by the pulse pressures 885-1 and 885-2, respectively. This causes acorresponding squeezing of the portion 910 and part of 920 (e.g., thelayer 850 and pyramids 890), as the film 835 is assumed to be fixed,e.g., to a watch or neckband or other wearable, and there is acorresponding capacitance change. Additionally, there is a capacitancechange in response to a return of the portion 910 (e.g., and part ofportion 920) to an original state. In this example, the pyramid base'swidth 825 is 10 μm, the distance 830 between edges of pyramids is 20 μm,distance 845 between a surface of a thin layer 846 of PDMS and a surfaceof the Cr/Au layer 850 is 7-8 μm, distance 870 between the PDMSmicrohairs 860 is 60-120 μm, hair length 880 of the PDMS microhairs 860is 150-450 μm, and diameter 875 (e.g., assuming the microhairs arecylindrical) of the PDMS microhairs 860 is 20-50 μm. The adhesive layerscan be made from a Phenoxy resin with a low molecular weight. See theInChem Corp online brochure on www.phenoxy.com. Furthermore, theelastomeric polymer (e.g., as used in the pyramids 890) may comprisepolydimethylsiloxane, the flexible polymer film (e.g., as used in thepolymer film 855) may comprise polyester, polyimide, polyethylene,polypropylene, polycarbonate, polyvinyl chloride, acrylic polymer,fluorinated polymer, polyethylene naphthalene or combination of two ormore of these polymers, and the adhesive may comprise Phenoxy resins orpolyvinyl alcohol.

In terms of the examples herein, it has been primarily assumed that onewave from an ECG would be used and one pulse wave from a pulse wavepressure sensor would also be used, where the pulse wave pressure sensorwas usually on the wrist. However, it is possible to determine the PTTand other information using two pulse wave sensors and the data fromthem. Turning to FIG. 8, this figure is a graph on the same time scaleof two different pulse waves, and illustrates determination of pulsetransit time (PTT) between heart and wrist and time difference between aforward wave point and the ending point of the wave (T₂). Thisparticular example uses radial artery pulse wave data 165-1, which ispulse wave data from the wrist. Also, another pulse wave 165-2 is shown,this one from the chest. The pulse transit time (PTT) 195 may bedetermined by comparing the maximum inclination 205 of the chest pulsewave data 165-2 and the corresponding maximum inclination 204 of theradial artery pulse wave data 165-1. The T₂ 197 is described above.

In this example, one of the pulse waves 165-1/165-2 is determined usinga pulse wave pressure sensor such as shown in FIG. 6 or 7, or a PPG. Theother pulse wave 165-1/165-2 may be determined using another pulse wavepressure sensor such as shown in FIG. 6 or 7, or a PPG or oximetersensor 175. The locations of the pulse waves from the chest or a neck oran arm close to the chest and the wrist or the finger are also merelyexemplary.

The following are additional examples.

A system with ECG, pulse wave sensors, and electronic hub can diagnosevarious cardiovascular diseases that include but are not limited to highblood pressure, hypertension, arrhythmias, pulse rates, sinus blocks,and pacemaker impulse. A system with ECG, pulse wave sensors, andadditional sensors such as a sound sensor, a strain gauge sensor, and/oran electromyography (EMG) sensor can act to provide more data withintegration to the electronic hub in support of continuous or timed orperiodic measurements and correlation with the heart, blood flow and/orblood pressure as well as other data that could aide modeling andanalytical characterization of the body.

Further, it is possible to use a controlled manual, semi-automated orautomated blood pressure wrist, arm, or other location blood pressuremonitor which can provide a secure position to begin an inflation stepof a bladder or cuff such that blood flow is altered or stopped for ashort time, followed by bladder pressure relief while sensorscharacterize the blood pressure and/or blood flow. Such a periodicmeasurement or measurements can aide in blood pressure calibration undercontrolled measurement conditions such as having a person or patientremain relatively still during this procedure. This may be performed ina doctor's office, for instance.

Further calibration of the relative stiffness of arteries and veins maybe determined via measurement of the pulse wave of blood flow withmultiple sensors such as those highlighted above and with blood pressuremeasurements due to a periodic, inflatable bladder to restrict bloodflow with increased pressure and measurement at elevated bladderpressure down through reduced or no bladder pressure while monitoringblood flow, relative pulse shape and/or blood pressure. Ultrasoundcharacterization between sensors may also be deployed to determinedistance between sensor on a person or other animals.

The system can incorporate encryption in system hardware, communicationsand use to provide security on personal information, tracking, recordingand access.

Use of one or more electrical contacts ECG and/or EMG sensors mayimprove quality of data. The one or more sensors may be on the body as awearable device adhesively joined in a temporary manor to the skin ormay be joined to or be part of clothing or other wearable solutions.

The pulse wave sensors may be on the body such as on the chest cavity orelsewhere as a wearable such as by using an adhesive to form a temporaryattachment to the skin, integrated into a shirt or attached to a shirt,pants, socks or other clothing, in a watch band or ankle bracelet. Theuse of two or more sensors may take advantage of ultrasound sensors orsound communication to provide reference of distance from one sensor toanother. For instance, when measuring the pulse transit time using anECG and a pulse wave sensor, there can be an error due to the differencebetween the heart's electrical R signal and the heart's ventricle valveopening as the ventricle muscle squeezes blood to make the valve open.The error can be limited if two pulse wave sensors instead of one ECGand one pulse wave sensor are used. However, it is not easy to employthe two pulse wave sensors due to signal detection issues.

One or more ECG and/or EMG sensors may be co-located in close proximitywith one or more pulse wave sensors such as at or near the heart, on thechest cavity, an arm(s), leg(s) or elsewhere on the body. One or moreECG and/or EMG sensors may be used, which are located remotely from thepulse wave sensor or sensors such as but not limited to on thetorso/chest cavity for ECG and or EMG and on legs and/or arms for pulsewave sensor(s). Data from ECG/EMG and pulse wave sensors can becommunicated between sensors and such data collection may be performedby, e.g., a microprocessor by wired communication, wirelesscommunication or both.

The blood pressure monitoring systems described above may be used withother sensors such as motion sensors, accelerometers, gyroscopicsensors, temperature sensors, humidity sensors, oxygen sensors, chemicalsensors, and the like. These sensors may be used on the body for clientevaluation in at least the following scenarios: while resting (e.g.,sleeping), lying down, sitting up, standing, as examples; whileexercising or moving such as walking, running, swimming; while understress such as at work, having a lack of sleep, and/or being indangerous environment; and relative to the environment, temperature,humidity, sea level high altitude, low oxygen, polluted air environment,chemical exposure and other environmental conditions.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device. A computer readable storage medium does notinclude a propagating wave.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on thedesigner's computer, partly on the designer's computer, as a stand-alonesoftware package, partly on the designer's computer and partly on aremote computer or entirely on the remote computer or server. In thelatter scenario, the remote computer may be connected to the designer'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider).

Aspects of the present invention are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The following abbreviations that may be found in the specificationand/or the drawing figures are defined as follows:

BDC body correlation factor

BP blood pressure

cm/ms centimeters per millisecond

CVD cardiovascular disease

DVP digital volume pulse

DBP diastolic blood pressure

EKG or ECG electrocardiogram

EMG electromyography

I/F interface

LAN local area network

LCD liquid crystal display

LED light emitting diode

mmHg millimeters of mercury

m/s meters per second

NW network

PPG photoplethysmography or photoplethysmogram

PTT pulse transit time

PWV pulse wave velocity

Rx receiver

SBP systolic blood pressure

SI stiffness index (e.g., in cm/ms)

Tx transmitter

WLAN wireless local area network

What is claimed is:
 1. An apparatus comprising: at least one pulse wavepressure sensor where pulse wave data is received from, whereinreceiving of the pulse wave data is via one of a wireless or wiredinterface, wherein the at least one pulse wave pressure sensor comprisesa layered structure configured, in response to pulse waves in a person,to generate electronic pulse waves in a form of a capacitance versustime; an electrocardiogram sensor where electrocardiogram data isreceived from, wherein the receiving of the electrocardiogram data isvia one of a wireless or wired interface; and one or more memoriesstoring computer readable code; and one or more processors, wherein theone or more processors, in response to loading and executing thecomputer readable code, cause the apparatus to perform operationscomprising: receiving electrocardiogram data comprising data from theelectrocardiogram sensor; receiving pulse wave data from the at leastone pulse wave pressure sensor, the pulse wave data comprising data fromone or more pulse waves from the person; determining blood pressureusing at least the electrocardiogram data and the pulse wave data; andoutputting an indication of the blood pressure.
 2. The apparatus ofclaim 1, wherein the at least one pulse wave pressure sensor furthercomprises: a sensor structure, comprising: a first portion configured tocontact the person at a skin surface of the person where the sensorstructure is capable of taking readings concerning arteries or veins orboth thereunder; a second portion that contacts the first portion and isconfigured to have a capacitance, wherein a pulse pressure under theskin causes squeezing or bending between the first portion and a fixedpart of the second portion, and wherein the first and second portionsare configured to create a capacitance change in response to thesqueezing or bending caused by the pulse pressure in relation to areturn to an original state of the first portion with a release of thepulse pressure; and circuitry connected to the sensor structure andconfigured to measure and transmit a waveform for the sensor structureand configured to digitize the measured waveform, wherein the waveformcaptures the capacitance change.
 3. The apparatus of claim 1, whereindetermining blood pressure using at least the electrocardiogram data andthe pulse wave data further comprises determining a systolic bloodpressure based on pulse transit time (PTT) (SBP_(PTT)) using thefollowing:SBP_(PTT) =a*ln(h ²/PTT²)+b, where h is the person's height, a and b areconstants which are empirically obtained, PTT is a pulse transit timedetermined using the electrocardiogram data and the pulse wave data, andln(⋅) means natural logarithm, and wherein PTT is determined as a timebetween an R peak in the electrocardiogram data and a correspondingmaximum inclination in pulse wave data from the at least one pulse wavepressure sensor.
 4. The apparatus of claim 3, wherein the one or moreprocessors, in response to loading and executing the computer readablecode, further cause the apparatus to perform operations comprising:outputting an indication of the systolic blood pressure based on pulsetransit time (PTT) (SBP_(PTT)), wherein the outputting is to one or moreof a display or a wireless or wired network interface.
 5. The apparatusof claim 3, further comprising one or more photoplethysmography sensors.6. The apparatus of claim 5, wherein at least one of the one or morephotoplethysmography sensors comprises a reflection-modephotoplethysmography sensor.
 7. The apparatus of claim 3, whereindetermining blood pressure using at least the electrocardiogram data andthe pulse wave data further comprises determining diastolic bloodpressure using the following:DBP=c*SBP_(PTT) +dT ₂ +e, where c, d and e are constants which areempirically obtained, and T₂ is determined using the pulse wave datafrom the at least one pulse wave pressure sensor and is a time intervalbetween a peak point of a pulse wave and a baseline point where thepulse wave reaches to the baseline.
 8. The apparatus of claim 7, whereinthe one or more processors, in response to loading and executing thecomputer readable code, further cause the apparatus to performoperations comprising: outputting one or more indications of one or moreof the following: the systolic blood pressure based on pulse transittime (PTT) (SBP_(PTT)) and the diastolic blood pressure, wherein theoutputting is to one or more of a display or a wireless or wiredinterface.
 9. The apparatus of claim 7, further comprising aphotoplethysmography sensor.
 10. The apparatus of claim 9, whereinphotoplethysmography sensor comprises a reflection-modephotoplethysmography sensor.
 11. The apparatus of claim 7, whereindetermining blood pressure using at least the electrocardiogram data andthe pulse wave sensor data further comprises: determining the systolicblood pressure using the following equation:SBP=SBP_(PTT)[1+α×SI_(DVP)], where SBP is systolic blood pressure,SBP_(PTT) is the systolic blood pressure based on the pulse transit time(PTT), α is defined empirically, and SI_(DVP) is a stiffness indexdetermined using the pulse wave data.
 12. The apparatus of claim 11,wherein the one or more processors, in response to loading and executingthe computer readable code, further cause the apparatus to performoperations comprising: outputting one or more indications of one or moreof the following: the systolic blood pressure based on pulse transittime (PTT) (SBP_(PTT)), diastolic blood pressure, and the systolic bloodpressure, wherein the outputting is to one or more of a display or awireless or wired network interface.
 13. The apparatus of claim 11,wherein the pulse wave data used for determination of the stiffnessindex is from a photoplethysmography sensor.
 14. The apparatus of claim13, where the photoplethysmography sensor comprises a reflection-modephotoplethysmography sensor.
 15. The apparatus of claim 11, wherein thestiffness index SI_(DVP) is determined using the following:${{SI}_{DVP} = \frac{height}{\Delta\; T_{DVP}}},$ where height is theheight of the person and ΔT_(DVP) is a time difference between a forwardwave point and a reflective wave point and is determined using the pulsewave data.
 16. The apparatus of claim 15, further comprising aphotoplethysmography sensor, and wherein the pulse wave data used fordetermination of the stiffness index is from the photoplethysmographysensor.
 17. The apparatus of claim 16, where the photoplethysmographysensor comprises a reflection-mode photoplethysmography sensor.
 18. Theapparatus of claim 15, wherein the one or more processors, in responseto loading and executing the computer readable code, further cause theapparatus to perform operations comprising: outputting one or moreindications of one or more of the following: the systolic blood pressurebased on pulse transit time (PTT) (SBP_(PTT)), diastolic blood pressure,the systolic blood pressure, and the stiffness index, wherein theoutputting is to one or more of a display or a wireless or wired networkinterface.
 19. An apparatus comprising: an electrocardiogram sensorconfigured to receive electrocardiogram data, the electrocardiogram datacomprising data from an electrocardiogram from a person; at least onepulse wave pressure sensor configured to receive pulse wave data fromone or more pulse waves of the person; one or more memories storingcomputer readable code; and one or more processors, wherein the one ormore processors, in response to loading and executing the computerreadable code, are configured to cause the apparatus to performoperations comprising: determining blood pressure, comprising:determining a systolic blood pressure based on pulse transit time(SBP_(PTT)) using the following:SBP_(PTT) =a*ln(h ²/PTT²)+b, where h is the person's height, a and b areconstants which are empirically obtained, PTT is a pulse transit timedetermined using the electrocardiogram data and the pulse wave data, andln( ) means natural logarithm, and wherein PTT is determined as a timebetween an R peak in the electrocardiogram data and a correspondingmaximum inclination in the pulse wave data, and outputting an indicationof the determined blood pressure.
 20. The apparatus of claim 19, whereinthe at least one pulse wave pressure sensor comprises a layeredstructure configured, in response to pulse waves in the person, togenerate electronic pulse waves in a form of a capacitance versus time.21. The apparatus of claim 19, wherein the at least one pulse wavepressure sensor further comprises: a sensor structure, comprising: afirst portion configured to contact the person at a skin surface of theperson where the sensor structure is capable of taking readingsconcerning arteries or veins or both thereunder; a second portion thatcontacts the first portion and is configured to have a capacitance,wherein a pulse pressure under the skin causes squeezing or bendingbetween the first portion and a fixed part of the second portion, andwherein the first and second portions are configured to create acapacitance change in response to the squeezing or bending caused by thepulse pressure in relation to a return to an original state of the firstportion with a release of the pulse pressure; and circuitry connected tothe sensor structure and configured to measure and transmit a waveformfor the sensor structure and configured to digitize the measuredwaveform, wherein the waveform captures the capacitance change.
 22. Theapparatus of claim 19, wherein determining blood pressure furthercomprises determining diastolic blood pressure using the following:DBP=c*SBP_(PTT) +dT ₂ +e, where c, d and e are constants which areempirically obtained, and T₂ is determined using the pulse wave datafrom the at least one pulse wave pressure sensor and is a time intervalbetween a peak point of a pulse wave in the pulse wave data and abaseline point where the pulse wave reaches to the baseline.